ewest: HABITAT is not a new herbicides by any means (over 15 yrs of field-use). However, its life as a registered aquatic plant control product is in its infancy. Accordingly, HABITAT's efficacy research on aquatic plants is relatively limited - and has primarily targeted the exotic or noxious plant species that pose the greatest problems (ie. represent the largest market potential) - and P. diversifolius doesn't fall within that group.

I have worked with HABITAT on several rooted-emergent species and found it to be much more effective than most of the standard alternatives. It also has a very desirable environmental "tox-profile" (meaning that it has very low vertebrate and invertebrate toxicity, including non-plant aquatic organisms - and has a relatively short half-life ~ is non-persistent in the environment).

All this to say that I'm not certain why you're seeing what you've witnessed, since I haven't worked with HABITAT on any of the pondweed species. That might change soon, since today I spoke with a pond owner who lives within a few miles of my house and has a 4+ acre pond with a high infestation of P. diversifolius.

In the mean time, my initial speculation is that you are using a "cheap" surfactant - or at least an inappropriate surfactant for HABITAT (Cide-Kick?). That speculation is based upon the spotting that you've observed after only 3 days (more or less). BTW: Cide-Kick is fine for applications with contact herbicides such as REWARD or AQUATHOL. These two herbicides work primarily through cellular disruption - so CIDE-KICK actually enhances that mode of action.

HABITAT's systemic mode of action is very slow (compared to other types of herbicides). I would not expect to see overly noticeable symptoms until a week or two after the application. Using a surfactant such as Cide-Kick II - or some cheap surfactant that is heavily loaded with isopropyl alcohol (IPA). IPA is often blended into many surfactants to lower the cost of production, since IPA can still be classified as an "active-ingredient". However, its presence may induce tissue damage to contacted leaf surfaces. Rapidly damaged or desiccated leaves - though they may excite the applicator - don't provide the best avenue for systemic herbicide uptake. Damaged leaf tissue may actually interfere with herbicide-transport and function within the plant's vascular system and physiology, respectively. Basically, you may forfeit some of the herbicides efficacy by using the improper surfactant.

In essence, use a quality surfactant with all systemic herbicides. The extra money invested in a good surfactant is more than compensated by the added performance from the much more expensive herbicide.

The HABITAT treatment shown in the posted pictures was applied on 29 Aug. I don't plan to check on its status until next Weds (2 weeks post-treatment). Even then, I only expect to see discolored alligator weed - not brown-out stalks.

I'll try to post again once I've had a chance to run some HABITAT plots on American pondweed. In the mean time, evaluate the surfactant that you're using to see if it might be causing any tissue damage (maybe even try treating some of your plants with only your surfactant in the mix - and no herbicide - to see if any leaf-spotting is observed).